In multi-station production lines, circuit boards are fed from one station to another, each station performing an operation on the circuit board, for example, applying or reading a bar code sticker on the board, populating the board with circuit elements, soldering the board, inspecting the board, etc. Each of the stations has a conveyor extending longitudinally from a receiving end to a location within the station at which the aforesaid operation is performed, and then to a discharge end. The conveyor forms a slot having a lateral width corresponding to the width of the circuit board. The circuit board is passed from the discharge end of the conveyor of one station to the receiving end of the conveyor of an adjacent downstream station. Thus, each station is downstream of those which previously acted on the circuit board, and is upstream of those which will act on the circuit board subsequently.
Advanced manufacturing techniques call for circuit board assembly lines to be adapted to handle circuit boards of varying widths. Thus, the conveyors of the individual processing stations should have an adjustable lateral width.
Existing automated systems provide a controller, such as a programmable logic controller (PLC), on each processing station to control various functions of the conveyor, including its lateral width. Each PLC is connected via a computer network to a master host computer. The host computer receives circuit board width information, for example, from a bar code reader, scanning circuit boards as they are fed to the production line. Additional bar code readers or other suitable means are required to track the location of each board as it proceeds through the production line. The host computer also tracks the width of each conveyor. When a board is processed which requires the conveyor at a given processing station to change width, the host computer must recognize the need to change width by linking the board with the location tracking information it receives. Upon recognizing a need to change conveyor width at a given processing station, the host computer sends a command to that station to actuate a conveyor width control mechanism. A signal is then passed to the host computer indicating that a width change has been completed. The host computer then sends another signal to the adjacent upstream processing station that the circuit board in question may be passed downstream. This control architecture is disadvantageousIy complex and computing-intensive. The complexity of the control architecture tends to increase production costs and the frequency and seriousness of control system failures.
Other known circuit board production line control systems having less complex computer control architecture, can only undergo width changes when the production line is completely empty of circuit boards. Thus, typically, only a single circuit board type or model can be processed in any period of time. To change conveyor width, the production line is allowed to empty and all production stations are then changed over simultaneously. This involves considerable production inefficiency, as all upstream processing stations must be idled while circuit boards of a previous model are conveyed through the last downstream processing station. Similarly, after width changeover, downstream processing stations sit idle awaiting the arrival of the new circuit boards.
It is an object of the present invention to provide a computer control system for a circuit board production line which allows automated conveyor width changeover of the individual processing stations of the production line, without the need for the complex control architecture based on a master host computer, and without requiting that the entire production line be emptied of circuit boards to permit conveyor width changes. Additional objects and advantages of the invention will be better understood from the following disclosure of the invention and detailed description of certain preferred embodiments.